I have two suggestions for you on how to filter that drush command. One is with pipes and grep. The other is with the option arguments.
First off I think you want drush pml (lowercase "L", not lowercase "I").
(1) Pipes and Grep
See the command below to list everything with status of "Not installed". The following may help give you a better picture of what's around your site. For example, here is what is there but "not installed" on my dev box.
$ drush pml | grep 'Not installed' | grep -v Core
Administration Actions permissions (VBO) (actions_permissions) Module Not installed 7.x-3.2
BackgroundField BackgroundField (backgroundfield) Module Not installed 7.x-1.5
Chaos tool suite Better Jump Menus (jump_menu) Module Not installed 7.x-1.4
Chaos tool suite Chaos Tools (CTools) AJAX Example (ctools_ajax_sample) Module Not installed 7.x-1.6
Chaos tool suite Chaos Tools (CTools) Plugin Example (ctools_plugin_example) Module Not installed 7.x-1.6
Chaos tool suite Custom content panes (ctools_custom_content) Module Not installed 7.x-1.6
Chaos tool suite Custom rulesets (ctools_access_ruleset) Module Not installed 7.x-1.6
Chaos tool suite Page manager existing pages (pm_existing_pages) Module Not installed 7.x-1.4
Chaos tool suite Stylizer (stylizer) Module Not installed 7.x-1.6
Chaos tool suite Term Depth access (term_depth) Module Not installed 7.x-1.6
Chaos tool suite Views content panes (views_content) Module Not installed 7.x-1.6
Taken individually that is
drush pml \ # Shows table of modules/themes and their status
| grep 'Not installed' \ # Filters for any line WITH 'Not installed'
| grep -v Core # Filters OUT any line containing string 'Core'
Given that you could do the following too :
$ drush pml | grep 'Enabled'
$ drush pml | grep 'Disabled'
(2) With options arguments to drush pml
You could also vary it up a bit with different arguments in the drush pml command
$ drush help pml
Show a list of available extensions (modules and themes).
Options:
--core Filter out extensions that are not in drupal core.
--no-core Filter out extensions that are provided by drupal core.
--package Filter by project packages. You can use multiple comma separated values. (i.e. --package="Core
- required,Other").
--pipe Returns a whitespace delimited list of the names of the resulting extensions.
--status=<disabled> Filter by extension status. Choices: enabled, disabled and/or 'not installed'. You can use
multiple comma separated values. (i.e. --status="disabled,not installed").
--type=<module> Filter by extension type. Choices: module, theme.
For example, you could use
$ drush pml --no-core --status="not installed" --type=module
Package Name Version
Administration Actions permissions (VBO) (actions_permissions) 7.x-3.2
BackgroundField BackgroundField (backgroundfield) 7.x-1.5
Chaos tool suite Better Jump Menus (jump_menu) 7.x-1.4
Chaos tool suite Chaos Tools (CTools) AJAX Example (ctools_ajax_sample) 7.x-1.6
***Note and caution:*** Always try this stuff on a development or vagrant box first. NEVER blindly do this to a production box.